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A technique for sanitizing sewagesludgeUrea treatment with dual advantages
2010 (English)Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
Abstract [en]

Sewage sludge contains valuable plant nutrients, which to a higher degree than the current

could be utilized in agriculture. First and foremost the phosphate contents in sewage sludge

could be an important contribution in the highly productive and resource demanding

agriculture of today. Only around 15 % of the sewage sludge produced in Sweden is currently

recycled to productive land.

There is in Sweden a political goal to recycle at least 60 % of the phosphorus in wastewater to

productive land by 2015, as stated in the Swedish Environmental Objectives. In the future

access to the currently most common phosphorus source in agriculture, easily mined

phosphate minerals, is thought to decrease.

Agricultural application of sewage sludge is however not an uncontroversial issue because of

the contaminants, mainly heavy metals, contained in sludge. Pathogens are another concern.

Upcoming legislation suggests sanitization requirements for sewage sludge used in

agriculture. This has previously not been required and might thereby create a market for new

solutions for sanitizing sludge.

The sanitization technique studied is addition of urea to sewage sludge. At sufficiently high

concentrations ammonia becomes toxic to microorganisms. Achieving sanitization through

urea treatment has previously been studied for various organic materials; such as source

separated dry material, co-compost and single use biodegradable toilets. The method has in

these studies been found effective.

This study was designed for evaluating application of urea at the inlet of decanter centrifuges

at sewage treatment plants, for the purpose of sanitization of the dewatered sludge. The

sanitizing effect after application of urea to dewatered sludge was studied separately.

The results indicate that addition of urea at the inlet of decanter centrifuges would cause a too

high ammonia concentration in the reject water. More than one fifth of the urea added ended

up in the liquid effluent which corresponded to reject water. The expected increase in nitrogen

load for sewage treatment plants was calculated to between 4 and 8 %. Addition of urea to

dewatered sludge caused a clear decrease in studied pathogens. Approximations of the costs

for sanitization of sludge by urea addition indicated that urea sanitization would be a low cost

method compared to liming, pasteurization and thermophilic anaerobic digestion.

Place, publisher, year, edition, pages
2010.
Series
UPTEC W, ISSN 1401-5765 ; 10 025
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:uu:diva-350594OAI: oai:DiVA.org:uu-350594DiVA, id: diva2:1205483
Educational program
Master Programme in Environmental and Water Engineering
Supervisors
Examiners
Available from: 2018-05-14 Created: 2018-05-14 Last updated: 2018-05-14Bibliographically approved

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CiteExportLink to record
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